There are many applications where one needs to determine range from the user's current location to a selected point. These applications include determining the range to a mark in sailboat racing, various other marine navigational situations, other recreational applications such as hiking, bird watching, orienteering, camping, cross country skiing, hunting and the like and various professional and military applications.
While a number of rangefinder devices currently exist, most are either relatively complex and expensive, requiring some degree of sophistication on the part of the user in order to achieve acceptable results; or, while simple, require that the user perform mathematical calculations to achieve range values.
A need therefore exists for a relatively simple, inexpensive rangefinder device which is relatively easy to use, providing rapid and accurate range values while requiring minimum sophistication and no calculations on the part of the user. In particular, most rangefinder devices operate by sighting on an object of known height at the distant point to which range is being determined and then utilizing the apparent height of this object to compute range. With existing devices, the user is frequently required to do a sighting, then look away to take readings from various displays or to do calculations and then back to do additional sightings. This multiple step procedure could be simplified if a heads-up display were provided which permitted the object being sighted on to be viewed through the display on which range and other values appear so that the user would be able to perform all required operations, and obtain a range indication, while continuously viewing the sighting object.